Plants can't move away from creatures that attack them: they have to stand and take it. But, they can readily regenerate large sections of themselves that are damaged. And too, over the hundreds of millions of years they have coexisted with animals, bacteria, viruses and fungi, they have developed a wide range of defensive strategies.
Obvious defences are thorns, spines, hairs, leathery leaves and so forth, but their chemical arsenal is even more impressive. Often passed on through family members, plants have developed a wide range of compounds that deter and sometimes poison those who venture to ingest them.
Plants have taken this situation further by also advertising tasty treats to attract pollinators and seed dispersers.
- Thus, fruit skin and flesh are usually coloured, and the flesh of most fruits is tasty and non-toxic: no point in poisoning the messenger.
- In contrast, valuable photosynthetic leaves, unripe fruits that contain immature seeds, bark that protects the stem, and storage roots often do contain potentially toxic compounds. However, we are now finding that many of these compounds, often in small amounts, have wide ranging medicinal and health benefits. But, in excess, can cause adverse reactions or even death.
Another factor, that has slowly changed over the millennia that people have gathered and cultivated foods is that, of course, we have picked the juiciest, sweetest, tastiest and least toxic plants to consume and cultivate. Hence, the majority of the plants we now eat are milder in flavour, are plumper, and have thinner rinds and skins. In the last few decades the rate of this change has escalated.
But there are negative consequences to this. Much of the compounds we have selectively excluded from these plants are also the ones that give the plant its resistance to attack by pests and diseases. Thus, partially accounting for why our tender veggies are so quickly ravaged by pests while the weeds that grow in profusion around them remain almost untouched. It also means that we do not consume anywhere near the amount of vitamins and secondary plant compounds our distant ancestors did.
Fortunately, many now realise the importance of saving heirloom food varieties, though sadly many have already disappeared.
- Almost 50% of the world's medicines are derived from plants and microbes.
- Yet, Edward O Wilson tells us that less than 3% of the flowering plants of the world have so far been analysed for their alkaloids, let alone other compounds.
- In contrast, bizarrely, particularly with the advent of genetic engineering, many plant-research teams are now focussed on producing new plants that contain many of the compounds we've bred out of them.
The vast potential of plant secondary compounds has been barely explored in the plants we know. This paucity of knowledge enlarges exponentially when we consider the many unexplored indigenous species worldwide. Frighteningly, many of these species are now on the verge or are already extinct.
A plant's defensive compounds act as their immune system.
- They include coumarins, terpenes, isothiocyanates (from brassicas), allicin, (from garlic) and alkaloids.
These compounds prevent maturation or reproduction of the pathogen, as well as puncturing their cell walls. They can also form a physical barrier against pathogenic invasion, and can initiate release of hormones (e.g. abscisic acid) that act as antibiotics and strengthen the plant against further attack.
And there are plant-attractor compounds, which include the colourful flavonoids and anthocyanins that develop within ripe fruits and flowers. Their aromas and colours are 'designed' to lure.
When we consume many of these compounds, they have anti-cancer properties, can act as antimicrobials, as anti-inflammatories, can enhance cardiovascular health, and boost the immune system.
- A recent study shows that weight, blood pressure, physical and emotional well-being, and quality of life, all significantly improved in a group of people who included elderberry fruits and flowers in their diet.
- Globe artichokes have liver-protective properties. This veggie also reduces digestive disorders such as loss of appetite, nausea, diarrhoea, irritable bowel syndrome.
- Lemon balm, as well as relieving agitation caused by dementia, has been shown to enhance and restore mental functions, including memory. It has helped children with sleep problems caused by ADHD.
- The odd combination of oregano and cranberries has been shown to be very effective at treating many bacterial and fungal infections: equally effective as antibiotics in some instances, but without the negatives.
- A large study has shown that daily consumption of small amounts of nettles resulted in 60% of patients ceasing to need non-steroidal anti-inflammatory drugs for their rheumatism.
- Passion-fruit juice is a proven natural sedative: given to people before surgery instead of a pre-med, it effectively reduces anxiety without any side effects.
- Prunes contain staggering amounts of antioxidants, higher than all other commercial fruits. These boost the immune system, reduce inflammation, fight cancer (e.g. breast, colon), reduce cardiovascular disease and stroke, help repair cell damage and slow the progression of age-related disorders.
- Rye enhances early insulin secretion in people susceptible to development of type-2 diabetes; thus, slowing onset of this disease.
- Greatly undervalued tamarind has been shown to lower 'bad' cholesterol (LDLs) by 73%, to lower triglycerides by 60%, plus increase 'good' cholesterol (HDLs) by 62%.
- A study reports that people who drank hot black tea, with lemon peel, were 70% less likely to develop skin cancer: drinking tea alone reduced the risk by 40%.
- Several studies report that lycopene-rich tomatoes can reduce the occurrence and impact of existing prostrate cancers by 30--40%.